1. Field of the Invention
This invention relates to a method for the production of an optically active (+)-4,4,4-trifluoro-3-(indole-3-butyric acid. More particularly, this invention relates to a method for the production of an optically active (+)-4,4,4,-trifluoro-3-(indole-3-)butyric acid having a strong action of promoting the elongation of plant roots, by preparing a 2,2,2-trifluoroethyl ester of 4,4,4-trifluoro-3-(indole-3-)butyric acid as a racemic modification and subjecting the ester to stereoselective hydrolysis using an enzyme.
The optically active (+)-4,4,4-trifluoro-3-(indole-3-)butyric acid (hereinafter referred to as "optically active (+)-TFIBA") is one of the fluorine-containing .beta.-indole butyric acids and has plant growth regulating activities such as the action of promoting the elongation of plant roots.
The optically active (+)-TFIBA is thus an important compound which functions as a plant growth regulating substance and can be extensively applied in agriculture and horticulture as for increasing crop yield and the cultivation of fruits.
2. Description of the Prior Art
As auxins, i.e. substances which promote the growth of plants, indole-3-acetic acid (IAA) and derivatives thereof (such as indole-3-methyl acetate and indole-3-acetamide) have been known for a long time.
Recently, such compounds as fluorine-containing .beta.-indole butyric acids have been developed. These compounds, i.e. 4,4,4-trifluoro-3-(indole-3-)butyric acid (hereinafter referred to as "TFIBA"), 4,4,4-trifluoro-2-hydroxy-3-(indole-3-)butyric acid, and 4,4,4-trifluoro-3-(indole-3-)butyronitrile, have been shown to have a strong action of promoting the elongation of plant roots (Japanese Patent Public Disclosure Hei 5-279331).
It is further known that the optically active (+)-TFIBA is obtained by causing an enzyme to react on an ethyl ester of a racemic modification TFIBA containing an asymmetric carbon atom thereby effecting selective hydrolysis of the ester and that this product of hydrolysis has a stronger action of promoting the elongation of roots than the racemic modification TFIBA. It is known that among enzymes studied to date, lipase PS, lipase AK, lipase AY, and protease M are suitable for producing the optically active (+)-TFIBA and that particularly when the lipase AK is used, the optically active (+)-TFIBA is formed at high stereoselectivity and high optical purity [Japanese Patent Public Disclosure Hei 6-56774, J. Fermentation and Bioengineering 76:178 (1993)].
The racemic modification TFIBA has a fairly strong action of promoting the elongation of plant roots as described above. It is known that the enzymatically divided optically active (+)-TFIBA has a still stronger activity, namely a still stronger action of promoting the elongation of roots. Since the conventional enzymatically dividing method is deficient in the reactivity between enzyme and substrate, it is therefore desired to establish a more efficient enzymatically dividing method.